All conventional audio and video tape cassettes have some form of erasure preventing mechanism to prevent previously recorded signals from being inadvertently erased. These mechanisms, also called recording lock out mechanisms, in their simplest form include a recess or cavity formed in the side wall of the cassette and a tab formed in the side wall and located to cover the cavity. When the tab covers the cavity, a detecting member of the cassette recorder permits recording on the tape. When the tab is removed, the detecting member prevents recording. After removal of the tab, in order to rerecord on the tape cassette, the recess must be covered using, for example, adhesive tape. However, this is cumbersome for the user.
U.S. Pat. No. 4,607,299 to Oishi et al., discloses a box-shaped member which slides within a space in the side wall of the cassette between first and second positions in which recording is prevented and permitted, respectively. The member includes side walls which are biased toward and frictionally engage the walls of the space to maintain the member in either the recording preventing or recording permitting position. However, other than this frictional engagement, there is no mechanism to prevent inadvertent sliding of the member between the two positions.
Another configuration for an erasure preventing button slidable within a cavity in the cassette side wall is shown in FIG. 1. As shown, the tape cassette 10 includes top, bottom, and side walls 12, 14, 16. A cavity 18 is formed in the side wall 16 and an opening 20 is formed in the side wall 16 adjacent the cavity 18. The erasure preventing button 30 is slidable within the cavity 18 between a released position and a depressed position. In the released position, recording is permitted and the button 30 engages the opening. In the depressed position, recording is prevented.
The erasure preventing button 30 of FIG. 1 includes a rectangular base 32 having a tab 34 to facilitate sliding the button 30 between the depressed and released positions. A rear arm 36 extends from the base 32 and prevents the erasure preventing button 30 from being removed from the cavity 18. The rear arm 36 culminates in a shoulder 38 which engages the end of a rear wall 22 of the cavity 18 to prevent the erasure preventing button 30 from being removed from the cavity. A rectangular front wall 40 perpendicular to the base 32 includes an arm 42 which is biased toward the opening 20. A shoulder 44 is formed on the arm 42 and extends into the opening 20 when the erasure preventing button 30 is in the released position. The surface 46 of the shoulder 44 facing away from the base 32 includes a curved convex surface 48 which frictionally engages one corner 24 of the opening 20 to resist sliding of the button 30 from the released position to the depressed position. However, the curved shape provides a wide range of varying resistance to sliding.